Electromagnetic signals exist across a large range of wavelengths. Electromagnetic signals include, for example, radio waves, visible light, X-rays, microwaves, infrared and ultraviolet waves. Electromagnetic signals can be used for a large variety of purposes in part because the various wavelengths of electromagnetic radiation interact with different materials in different ways. In fact, many materials (e.g, semiconductor lasers, Bragg reflectors, optical films, antennas) are designed to interact with electromagnetic waves in certain ways to produce certain results.
Metamaterials constitute another class of materials that are designed to interact with electromagnetic waves in specific ways. Metamaterials, in fact, can be configured to interact with electromagnetic signals in ways that other materials do not. Metamaterials may exhibit properties that may not ordinarily be present in other materials. For instance, metamaterials may exhibit a negative refractive index. This property, among others, opens up a new area of research and development.
Small-scale antennas is another class of materials that are designed to interact with electromagnetic waves in specific ways. Generally, an antenna is a device that transmits and/or receives electromagnetic waves. To operate efficiently, the antenna often has a size that is related to the wavelength of the signal being received/transmitted. Usually, the dimensions of the antenna are smaller than the wavelength of interest. It becomes increasingly difficult to construct antennas that are suitable for wavelengths that have small wavelengths.
The manufacture of small-scale structures such as metamaterials and nano-antennas, particularly with regard to shorter wavelengths, faces several challenges. For some purposes, metamaterials are limited in the sense that they can only operate effectively with larger wavelengths. In other words, the size of the metamaterial may impact which wavelengths can be used beneficially. As wavelengths become shorter, it becomes increasingly difficult to construct small-scale structures with resonators that are sufficiently small.
In addition, the fabrication of metamaterials is impacted by conventional lithography techniques, which are limited to planar patterns. Immersion lithography, nano-imprint lithography, and e-beam lithography, for example, are capable of printing small features. However, these lithography techniques are also planar in nature and are limited with respect to three-dimensional structures.